There is a travel drive system for this sort of work vehicles known in the related art, which includes a hydrostatic transmission (HST) travel circuit where a hydraulic pump is connected to a hydraulic motor by a closed circuit for transmitting a driving force by the hydraulic motor to wheels via a propeller shaft so as to allow the vehicle to be driven (refer to, for example, patent reference literature 1).
Patent reference literature 1: Japanese Laid Open Patent Publication No. H5-306768